Conventional wireless networks support priority-based reselection (PBR) operations, in which a user equipment (or mobile device) accessing a first cell re-selects to a second cell. A priority-based reselection operation uses priority information in its algorithm to choose the second cell. The priority information may be common priority information that is common to multiple user equipment or may be dedicated priority information that is device-specific to a particular user equipment.
In a priority-based reselection algorithm, an initial ranking of neighboring cells may be done based on assigned priorities rather than on relative or absolute radio measurement. It is possible to assign device-specific priority information, which persists across multiple cells, including cells of different radio access technologies (RATs). Reselection algorithms are typically based on measured properties of a signal associated with a particular cell. For example, for a GSM cell, measurements of the signal transmitted on the broadcast control channel (BCCH) frequency for that cell may be used for a PBR algorithm.
In earlier reselection algorithms, a wireless device often made such measurements for multiple (possibly all) candidate cells. This often required measurements and comparisons of values for cells using different radio access technologies. As the numbers and types of cells increase (e.g., introduction of new radio access technologies), such a re-selection algorithm becomes progressively more complex. First, there are more candidate neighbor cells to evaluate. Also, it becomes harder to define appropriate ways of comparing measurements of cells that operate using different radio access technologies.
Additionally, the mobility of user mobile devices increases the number of reselection and handover operations and increases the number and frequency of cell searches accordingly. Previous changes in Release 10 (Rel-10) of 3GPP mandate a high priority search within a short time period of entering CELL_PCH state, URA_PCH state, or IDLE state. While this potentially speeds up a reselection to a higher priority layer by avoiding the possibility that the user equipment waits so long to perform the search that it enters a non-idle state first, it also imposes unreasonable searching requirements on user equipment that enter and leave these states frequently.